In recent years, multi-layer laminated structures such as multi-layer vessels and multi-layer sheets, which comprises saponified products of ethylene-vinyl acetate copolymers or polyamide based resins as a barrier layer, and a polyolefin as the outermost layer, are gradually being employed for applications which have conventionally used metals.
For example, in view of a lighter weight, a greater capacity, ease of molding, and rust resistance, in the case vehicle fuel vessels and drums, the change from metal tanks to synthetic resin tanks is occurring rapidly.
In particular, synthetic resin fuel vessels are required to have resistance to fuel oil, impact resistance and adhesion durability. For synthetic resin fuel vessels which satisfy these requirements, multi-layer laminated structures comprising a layer made of a barrier material such as a saponified product of an ethylene-vinyl acetate copolymer, or a polyamide resin, which provides an excellent barrier to penetration by gases or liquids, and a layer made of a high density polyethylene resin, which offers excellent mechanical characteristics, laminated together are now in widespread use.
In addition, in recent years the performance requirements for fuel vessels have been tightened even further. For example, long term maintenance of performance for the so-called “15 years, 150,000 miles” period is now required. Examples of the specifics of the performance requirements which must be maintained for this long period include no peeling of individual layers of the multi-layer laminated structure, no deterioration or layer abnormalities within the barrier layer in order to prevent volatilization of fuel components into the atmosphere, no fuel volatilization arising from peeling of the pinch off section produced by a die cutter during the blow molding process, and maintenance of the low temperature impact resistance above a certain level in order to minimize damage caused by a collision or the like.
However, barrier materials such as saponified products of ethylene-vinyl acetate copolymers or polyamide based resins and polyethylene resins display almost no natural adhesion, and consequently during lamination of these resins, an adhesive resin with good adhesion to both layers must be used.
Examples of this type of adhesive resin composition include resin compositions comprising a polyolefin based polymer modified with a solid rubber as disclosed in Japanese Unexamined Patent Application, First Publication No. Sho 50-7847 and resin compositions comprising an ethylene/α-olefin copolymer rubber modified with an unsaturated carboxylic acid as disclosed in Japanese Unexamined Patent Application, First Publication No. Sho 52-49289.
Furthermore, in order to improve thermal stability and prevent apparatus corrosion, these compositions typically also contain antioxidants and acid absorbers. Phenol based antioxidants or phosphorus based antioxidants are usually used to improve the thermal stability, and metal slats of fatty acids such as calcium stearate or the like is usually used to prevent apparatus corrosion.
However, although the above compositions provide a certain degree of adhesive strength, the adhesive strength is not entirely satisfactory for modern high speed molding or for thin film sections such as vessel pinch off sections generated during rapid deformations during molding. In addition, when soaked in fuel such as gasoline, which represents an actual potential application, there was a significant decrease in adhesive strength.
Furthermore, in those cases in which these types of adhesive resin compositions were used, if the burrs and unused parison and the like produced as by-products during the molding of a large vessel or sheet are returned to the process and used as a regrind layer, then because the compatible of these by-products with the major constituents, namely the polyethylene resin and the barrier materials such as the saponified product of an ethylene-vinyl acetate copolymer or the polyamide based resin, is unsatisfactory, the low temperature impact resistance of the multi-layer vessel itself may deteriorate.
An object of the present invention is to provide an adhesive resin composition which displays excellent adhesive strength on bonding to a barrier material, during initial adhesion, durable adhesion, and even after soak in fuel oil, and which also has excellent moldability. Furthermore, another object of the present invention is to provide an adhesive resin composition which when recycled, displays good compatible in a regrind layer with polyethylene resins and barrier materials such as saponified products of ethylene-vinyl acetate copolymers or polyamide based resins, and which is consequently capable of suppressing deterioration in the low temperature impact resistance of a multi-layer vessel comprising a regrind layer. In addition, yet another object of the present invention is to provide a multi-layer laminated structure with excellent low temperature impact resistance formed using such an adhesive resin composition.